28F128J3A, 28F640J3A, 28F320J3A
22
Preliminary
4.5
Clear Status Register Command
Status register bits SR.5, SR.4, SR.3, and SR.1 are set to
“
1
”
s by the WSM and can only be reset by
the Clear Status Register command. These bits indicate various failure conditions (see
Table 16
).
By allowing system software to reset these bits, several operations (such as cumulatively erasing or
locking multiple blocks or writing several bytes in sequence) may be performed. The status register
may be polled to determine if an error occurred during the sequence.
To clear the status register, the Clear Status Register command (50H) is written. It functions
independently of the applied V
PEN
voltage. The Clear Status Register command is only valid when
the WSM is off or the device is suspended.
4.6
Block Erase Command
Erase is executed one block at a time and initiated by a two-cycle command. A block erase setup is
first written, followed by an block erase confirm. This command sequence requires an appropriate
address within the block to be erased (erase changes all block data to FFH). Block preconditioning,
erase, and verify are handled internally by the WSM (invisible to the system). After the two-cycle
block erase sequence is written, the device automatically outputs status register data when read (see
Figure 10,
“
Block Erase Flowchart
”
on page 33
). The CPU can detect block erase completion by
analyzing the output of the STS pin or status register bit SR.7. Toggle OE#, CE
0
, CE
1
, or CE
2
to
update the status register.
When the block erase is complete, status register bit SR.5 should be checked. If a block erase error
is detected, the status register should be cleared before system software attempts corrective actions.
The CUI remains in read status register mode until a new command is issued.
This two-step command sequence of set-up followed by execution ensures that block contents are
not accidentally erased. An invalid Block Erase command sequence will result in both status
register bits SR.4 and SR.5 being set to
“
1.
”
Also, reliable block erasure can only occur when V
CC
is valid and V
PEN
= V
PENH
. If block erase is attempted while V
PEN
≤
V
PENLK
, SR.3 and SR.5 will
be set to
“
1.
”
Successful block erase requires that the corresponding block lock-bit be cleared. If
block erase is attempted when the corresponding block lock-bit is set, SR.1 and SR.5 will be set to
“
1.
”
4.7
Block Erase Suspend Command
The Block Erase Suspend command allows block-erase interruption to read or program data in
another block of memory. Once the block erase process starts, writing the Block Erase Suspend
command requests that the WSM suspend the block erase sequence at a predetermined point in the
algorithm. The device outputs status register data when read after the Block Erase Suspend
command is written. Polling status register bit SR.7 then SR.6 can determine when the block erase
operation has been suspended (both will be set to
“
1
”
). In default mode, STS will also transition to
V
OH
. Specification t
WHRH
defines the block erase suspend latency.
At this point, a Read Array command can be written to read data from blocks other than that which
is suspended. A program command sequence can also be issued during erase suspend to program
data in other blocks. During a program operation with block erase suspended, status register bit
SR.7 will return to
“
0
”
and STS output (in default mode) will transition to V
OL
. However, SR.6
will remain
“
1
”
to indicate block erase suspend status. Using the Program Suspend command, a
program operation can also be suspended. Resuming a suspended programming operation by